dm: fix missed error code if .end_io isn't implemented by target_type

dm: fix missed error code if .end_io isn't implemented by target_type

commit 5164bece1673cdf04782f8ed3fba70743700f5da upstream.

In bio-based DM's clone_endio(), when target_type doesn't implement
.end_io (e.g. linear) r will be always be initialized 0.  So if a
WRITE SAME bio fails WRITE SAME will not be disabled as intended.

Fix this by initializing r to error, rather than 0, in clone_endio().

Signed-off-by: Alex Chen <alex.chen@huawei.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Fixes: 7eee4ae2db ("dm: disable WRITE SAME if it fails")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>